Average sea-ice concentration for each month, in ice-chart colours. Step through months and years, press play, or compare one month across every year.
Share of seasons in which water at or below the chosen ice limit, open to the sea, came within the chosen distance of Koether Inlet. Each point pools ±3 days.
Each row is one season, 1 November to 31 March. Colour shows how close workable water came to the inlet that day. Select a row to open it below.
Average width of the band of fast ice along the coast within 50 km of the inlet, per 15-day window. Grey: MODIS maps of Fraser et al., 2000 to 2018. Blue: Sentinel-1 classifier trained on those maps, carrying the record on from 2018/19 to 2025/26. The shaded window holds the 23 January target.
Workable water. Ice limits are planning yardsticks: 3/10 is open drift, 6/10 is workable for a Polar Class 5 or 6 ship, 8/10 needs real icebreaking. Check them against the chosen ship's POLARIS assessment.
Closest approach. Straight-line distance from the inlet to the nearest such water that connects to open sea north of 68°S. A helicopter flies the straight line; the ship's track through leads is longer.
Which record to trust. AMSR2 (3 km) is the main record since 2012. The 25 km NSIDC record extends back to 1979 but blurs the coast. US National Ice Center charts, shown as dots, read the coast as closed more often; radar and MODIS imagery sided with AMSR2 in the seasons where they disagree (2015/16, 2016/17).
Limits. Passive microwave under-reads wet summer ice, so odds lean optimistic. Fast ice inside about 10 km of the coast is invisible to it, which is why the fast-ice record is shown separately.
Sources. Bremen ASI AMSR2 v5.4 · NOAA/NSIDC CDR G02202 v6 · US National Ice Center charts · Fraser et al. fast ice v2.2 · Sentinel-1 GRD.
Fast-ice classifier skill. Tested on seasons it was not trained on, the Sentinel-1 maps overlap the MODIS maps by about half (intersection over union 0.5). Use it for the size of the band, not for its exact edge on a given day.